Arkan, Hero of the Storm

Prowess
Sorcery spells you control have Flash. At the beginning of your end step, if you casted three or more instant or sorcery spells, transform Arkan, Hero of the Storm into an Enchantment. Creatures you control have prowess, and Arkan, Hero of the Storm is a Creature as long as you have 10 or more Instant and Sorcery cards in your graveyard or Exile. It also gets +X/+0 for each sorcery card you own in Exile, and +0/+X for each Instant card you own in Exile.